Multiple evaporator refrigeration systems



United States Patent 3,350,896 MULTIPLE EVAPORATOR REFRIGERATION SYSTEMSJames R. Hamish, Staunton, Va., assignor to Westinghouse ElectricCorporation, Pittsburgh, Pa., a corporation of Pennsylvania Filed Jan.11, 1966, Ser. No. 519,877 7 Claims. (Cl. 62200) ABSTRACT OF THEDISCLOSURE In a refrigeration system having a plurality of evaporators,all of the evaporators are fed by a single expansion valve throughsolenoid-controlled valves. Local thermostats control the solenoids toopen the respective solenoidcontrolled valves when cooling is required.The expansion valve meters refrigerant to the active evaporator orevaporators at the rate at which the refrigerant is condensed,overfeeding the active evaporator or evaporators so gas and unevaporatedrefrigerant flow from the latter into an accumulator means in whichliquid refrigerant is evaporated by heat from the condensed refrigerantflowing to the expansion valve.

This invention relates to refrigeration systems having multipleevaporators, and has as objects to simplify and to improve theperformances of such systems.

As disclosed on pages 404-405 of the textbook Principles ofRefrigeration? by R. J. Dossat,published in 1961 by John Wiley & Sons,in refrigeration systems having multiple evaporators cut in and out bysolenoid controlled valves, a thermal expansion valve is usuallyprovided for each evaporator. Such expansion valves operate to maintainconstant degrees of superheat at the outlets of their respectiveevaporators so that all of the refrigerant supplied to the evaporators,is evaporated. Other refrigeration systems include refrigerant pumps tocirculate excess liquid refrigerant through multiple evaporators so thatnone of the evaporator surfaces is wasted to provide superheat, andrefrigerant distribution between evaporators is less critical. However,a refrigerant pump should be of the hermetic type to avoid leaks, andit, combined with its operating accessories, is expensive and requiresperiodic maintenance. Furthermore, since such a pump circulates nearlysaturated liquid, cavitation frequently occurs at the impeller, due tochanging suction pressure, and its life is relatively short.

This invention requires no refrigerant pump, and uses a single expansionvalve to overfeed a plurality of evaporators, the unevaporatedrefrigerant from the evaporators flowing into an accumulator where it isevaporated by heat from a' coil through which the high pressurerefrigerant liquid flows on its way to the expansion valve. Preferably,the expansion valve is a subcooling control valve which supplies to theactive evaporators, refrigerant liquid at the rate at which the latteris condensed while providing subcooling of such liquid. Among theadvantages of this invention, in addition to requiring but a singleexpansion valve, and not requiring a refrigerant pump, are that theinternal surfaces of the evaporators are thoroughly wetted, resulting inincreased heat transfer and efficiency. Oil return from the evaporatorsis less difiicult than in systems with thermal expansion valves sincethe excess refrigerant liquid fed to the evaporators washes theevaporator oil into an accumulator from which it can readily be returnedto the associated compressor. Where an air cooled condenser is used, theexpansion valve supplies sufiicient refrigerant to the active evaporatoror evaporators at low outdoor ambient temperatures when the condensingpressure would be too 3,350,896 Patented Nov. 7, 1967 valve of FIG. 1.

A refrigerant compressor C, driven by an electric motor CM, is connectedby discharge gas tube 10 containing a high pressure cut-out HPC, to oneend of condenser 11. The other end of the condenser 11 is connected byliquid tube 12 to the inlet end of heat exchange coil 14 withinaccumulator 15. The outlet end of the coil 14 is connected by tube 16 totube 19 containing subcooling control valve 17 which is the expansionvalve of the system. The tube 19 at the outlet side of the valve 17 isalso connected to tube 18 containing a valve VA, adjusted by a solenoidSA, and a hand adjustable valve 20, to one end of evaporator EA; isconnected by tube 21 containing a valve VB, adjusted by a solenoid SB,and a hand adjustable valve 22 to one end of evaporator EB, and isconnected by tube 24 containing a valve VC, adjusted by a solenoid SC,and a hand adjustable valve 25 to one end of evaporator EC. The otherends of the evaporators EA, EB and EC are connected by tube 27 to thetop of the accumulator 15. A U-shaped tube 28 within the accumulator 15has an open end 29, and its other end is connected by suction gas tube30, containing a suction pressure control SPC, to the suction side ofthe compressor C. Portions of the tubes .12 and 30 are in heat exchangecontact.

The hand adjustable valves 20, 22 and 25 are for permitting theevaporators EA, EB, and EC respectively, to be adjusted to suitoperating conditions.

The compressor C has cylinders CL1, CL2, CL3 and CL4, with heads H1, H2,H3 and H4 respectively. The plungers of solenoids S2, S3 and S4 extendinto the heads H2, H3 and H4 respectively, to depress the usual suctionvalve reeds which are not shown, for unloading the cylinders CL2, CL3and CL4 respectively. When the solenoids S2, S3 and S4 are energized,they withdraw their plungers, permitting the suction valve reeds toclose during the suction strokes of the respective pistons in therespective cylinders for loading the respective cylinders. The suctionpressure control SPC has a plunger 35 pivoted to switch blade 36 betweenthe ends of the latter. The blade 36 is pivoted at one end to fixedsupport 37, and its other end is curved so as to contact in succession,switch contacts 38, 39 and 40 which are in a correspondingly curvedpath, on increases in suction pressure. The contact 38 is connected toone end of the solenoid S2, the other end of which is connected toelectric supply line L2.'The contact 39 is connected to one end of thesolenoid S3, the other end of which is connected to the line L2. Thecontact 40 is connected to one end of the solenoid S4, the other end ofwhich is connected to the line L2. The switch blade 36 is connected toelectric supply line L1.

The solenoid SA is connected at one end to the line L2, and its otherend is connected to one end of thermostat TA, the other end of which isconnected to the line L1. The solenoid SB is connected at one to theline L2, and its other end is connected to one end of thermostat TB, theother end of which is connected to the line L1. The solenoid SC isconnected at one end to the line L2, and its other end is connected toone end of thermostat TC, the other end of which is connected to theline L1. The evaporators EA, EB and EC may be air cooling coils locatedin diiferent spaces to be ooled, and the thermostats TA, TB and TC maybe space thermostats.

Starter MS of the compressor motor CM, has an energizing winding 45connected at one to the line L2, and connected at its other end by wire46 to switch HPCS of the cut-out HPC. The switch HPCS is connected bywire 47 to outdoor thermostat ODT which is connected to the line L1.Thus, the winding 45 is connected in series with the switch I-lPCS andthe thermostat ODT to the lines L1 and L2. The motor CM is connecteddirectly to the line L2, and is connected through switch MSS of thestarter MS to the line L1.

The subcooling control valve 17, shown in detail by FIG. 2, has adiaphragm chamber 50 with a diaphragm 51 extending across its center.The chamber 50 above the diaphragm 51 is connected by capillary tube 52to thermal bulb 53 in heat exchange contact with the liquid tube 12. Thechamber 50 below the diaphragm 51 is connected by capillary tube 54 tothe interior of the tube 12. The valve 17 has a valve chamber 55 belowthe diaphragm chamber 50, with a partition 56 extending across itsinterior between its inlet and outlet. The partition 56 has a valveopening 57. The top of a piston rod 58 is attached to the center of thediaphragm 51, and its bottom is attached to a valve piston 59 above theopening 57. A coiled spring 60 extends around the rod 58 between thebottom of the diaphragm chamber 50 and the top of the piston 59, andbiases the latter towards the opening 57. An increase in the temperatureof the liquid flowing through the tube 12 into the coil 14 tends toadjust the valve 17 towards closed position, while an increase in thepressure of the same liquid tends to adjust the valve 17 towards itsopen position. For an increase in the rate at which refrigerant iscon-densed, if the valve 17 is not sufiiciently open, liquid will backup in the condenser 11 until the pressure has increased sufficiently orthe temperature has reduced sufficiently to cause the valve 17 to openfurther. When the condensing rate changes, the valve 17 readjustsaccordingly as do all modulating expansion valves, but it metersrefrigerant to the active evaporator or evaporators at the rate at whichrefrigerant is condensed as does a conventional pilot operated expansionvalve controlled by a pilot high pressure float. The subcooling controlvalve is preferred since it maintains a predetermined amount ofsubcooling in the condensed refrigerant, which may be, for example, F.subcooling at a condensing temperature of 100 F.

Operation When the outdoor temperature increases to a predeterminedtemperature, the outdoor thermostat ODT energizes through the closedswitch HPCS of the cut-out HPC, the starter MS which closes its switchMSS, energizing the compressor motor CM, and starting the compressor C.The latter supplies discharge gas through the tube 10 and the cut-outHPC to the condenser 11. Refrigerant liquid flows from the latter,through the tube 12, the coil 14 within the accumulator 15, thesubcooling control valve 17 and the tube 19 into the active evaporatoror active evaporators. If the thermostat TA is calling for cooling, itenergizes the solenoid SA which opens the valve VA to supply refrigerantto the evaporator EA. If the thermostat TB is calling for cooling, itenergizes the solenoid SB which opens the valve VB to supply refrigerantto the evaporator EB. If the thermostat TC is calling for cooling, itenergizes the solenoid SC which opens the valve VC to supply refrigerantto the evaporator EC. The valve 17 overfeeds the active evaporator orevaporators, gas and unevaporated refrigerant flowing from each activeevaporator through the tube 27 into the accumulator 15. Gas separatedfrom the liquid within the latter flows into the open end 29 of the tube28 into the latter, and then through the suction gas tube 30 to thesuction side of the compressor C. Heat from the liquid flowing throughthe coil 14 in contact with the liquid within the accumulator evaporatesthe refrigerant liquid flowing from the active evaporator or evaporatorsinto the accumulator, the liquid flowing through the coil 14 beingsubcooled by this action. Any refrigerant liquid which may enter thesuction gas tube 30 will be evaporated by heat from that portion of thetube 12 which is in heat exchange contact with the tube 30, the liquidflowing through the tube 12 being further subcooled by this action.

At its minimum load, the compressor C will operate with its cylinder CL1loaded and its other cylinders unloaded. As the load increases, thesuction gas pressure will increase, and the switch blade 36 of thecontrol SPC will move against the contact 38 to energize the solenoid S2which will withdraw its plunger to load the compressor cylinder CLZ. Ona further increase in load, a further increase in the suction gaspressure will cause the switch blade 36 to move against the contact 39to energize the solenoid S3 which will withdraw its plunger to load thecompressor cylinder GL3. On a further increase in the load, theincreased suction gas pressure will cause the switch blade 36 to moveagainst the contact 40 to energize the solenoid S4 which will withdrawits plunger to load the compressor cylinder CL4.

If the thermostat ODT should start the compressor when none of thethermostats TA, TB or TC is calling for cooling, the suction gaspressure would decrease below normal, and the usual low pressure cut-outwhich is not shown, would open its switch, stopping the compressormotor.

While the subcooling control valve disclosed herein is a direct actingone, it could, and for relatively large systems, would be a pilotoperated valve such as is disclosed in my copending application, Ser.No. 508,736, filed Nov. 19, 1965, for Controls for Refrigeration Systemsnow Patent No. 3,320,763 issued May 23, 1967.

What is claimed is:

1. A refrigeration system comprising a refrigerant compressor, acondenser, accumulator means, a heat exchange coil arranged to heatliquid Within said accumulator means, an expansion valve, a dischargegas tube connecting the discharge side of said compressor to saidcondenser, a liquid tube connecting said condenser to said coil, a thirdtube connecting said coil to the inlet of said expansion valve, a fourthtube connected to the outlet of said expansion valve, 21 fifth tubeconnected to said accumulator means, first and second fluid coolingevaporators connected at their outlet ends to said fifth tube, a suctiongas tube connecting said accumulator means to the inlet of saidcompressor, a tube containing a first valve connecting the inlet end ofsaid first evaporator to said fourth tube, a tube containing a secondvalve connecting the inlet end of said second evaporator to said fourthtube, a first thermostat responsive to the temperature of the fluidcooled by said first evaporator, means including said thermostat foropening said first valve when said first thermostat calls for cooling, asecond thermostat responsive to the temperature of the fluid cooled bysaid second evaporator, means including said second thermostat foropening said second valve when said second thermostat calls for cooling,and means for adjusting said expansion valve to supply refrigerant fromsaid coil into said fourth tube at the rate at which refrigerant iscondensed in said condenser.

2. A refrigeration system as claimed in claim 1 in which said expansionvalve is a subcooling control valve, and in which said means foradjusting said expansion valve responds to the pressure and thetemperature of the liquid flowing through said liquid tube.

3. A refrigeration system as claimed in claim 2 in which said means foropening said first valve comprises a solenoid, and includes meansincluding said first thermostat for energizing said solenoid; and inwhich said means for opening said second valve comprises a secondsolenoid, and includes means including said second thermostat forenergizing said second solenoid.

4. A refrigeration system as claimed in claim 1 in which said means foropening said first valve comprises a solenoid, and includes meansincluding said first thermostat for energizing said solenoid; and inwhich said means for opening said second valve comprises a secondsolenoid, and includes means including said second thermostat forenergizing said second solenoid.

5. A refrigeration system as claimed in claim 4 in which said tubecontaining said first valve also includes a throttling valve, and inwhich said tube containing said second valve also includes a throttlingvalve.

6. A refrigeration system as claimed in claim 1 in which said tubecontaining said first valve also includes 6 a throttling valve, and inwhich said tube containing said second valve also includes a throttlingvalve.

7. A refrigeration system as claimed in claim 6 in which said expansionvalve is a subcooling control valve, and in which said means foradjusting said expansion valve responds to the pressure and thetemperature of the liquid flowing through said liquid tube.

References Cited UNITED STATES PATENTS 2,472,729 6/1949 Sidell 62503 X3,234,752 2/1966 Quick 62196 X MEYER PERLIN, Primary Examiner.

1. A REFRIGERATION SYSTEM COMPRISING A REFRIGERANT COMPRESSOR, ACONDENSER, ACCUMULATOR MEANS, A HEAT EXCHANGE COIL ARRANGED TO HEATLIQUID WITHIN SAID ACCUMULATOR MEANS, AN EXPANSION VALVE, A DISCHARGEGAS TUBE CONNECTING THE DISCHARGE SIDE OF SAID COMPRESSOR TO SAIDCONDENSER, A LIQUID TUBE CONNECTING SAID CONDENSER TO SAID COIL, A THIRDTUBE CONNECTING SAID COIL TO THE INLET OF SAID EXPANSION VALVE, A FOURTHTUBE CONNECTED TO THE OUTLET OF SAID EXPANSION VALVE, A FIFTH TUBECONNECTED TO SAID ACCUMULATOR MEANS, FIRST AND SECOND FLUID COOLINGEVAPORATORS CONNECTED AT THEIR OUTLET ENDS TO SAID FIFTH TUBE, A SUCTIONGAS TUBE CONNECTING SAID ACCUMULATOR MEANS TO THE INLET OF SAIDCOMPRESSOR, A TUBE CONTAINING A FIRST VALVE CONNECTING THE INLET END OFSAID FIRST EVAPORATOR TO SAID FOURTH TUBE, A TUBE CONTAINING A SECONDVALVE CONNECTING THE INLET END OF SAID SECOND EVAPORATOR TO SAID FOURTHTUBE, A FIRST THERMOSTAT RESPONSIVE TO THE TEMPERATURE OF THE FLUIDCOOLED BY SAID FIRST EVAPORATOR, MEANS INCLUDING SAID THERMOSTAT FOROPENING SAID FIRST VALVE WHEN SAID FIRST THERMOSTAT CALLS FOR COOLING, ASECOND THERMOSTAT RESPONSIVE TO THE TEMPERATURE OF THE FLUID COOLED BYSAID SECOND EVAPORATOR, MEANS INCLUDING SAID SECOND THERMOSTAT FOROPENING SAID SECOND VALVE WHEN SAID SECOND THERMOSTAT CALLS FOR COOLING,AND MEANS FOR ADJUSTING SAID EXPANSION VALVE TO SUPPLY REFRIGERANT FROMSAID COIL INTO SAID FOURTH TUBE AT THE RATE AT WHICH REFRIGERANT ISCONDENSED IN SAID CONDENSER.